Trans-2,2-dimethyl-3-formylcyclopropanecarboxylic acid esters are useful compounds as intermediates of insecticides (e.g. J. Chem. Soc. (C), 1076 (1970)). As processes for production of the trans-2,2-dimethyl-3-formylcyclopropanecarboxylic acid ester, J. Chem. Soc. (C), 1076 (1970) discloses a process comprising oxidizing trans-chrysanthemic acid with ozone, and Tetrahedron, 57, 6083 (2001) discloses a process comprising treating a trans-2,2-dimethyl-3-(acyloxymethyl)cyclopropanecarboxylic acid ester with a base followed by conducting Swern oxidation.